1. Field of the Invention
The present invention relates to an explosively insensitive ignitor apparatus and method for igniting a propellant.
2. Description of the Prior Art
Propellants have been ignited with primary explosives which are sensitive explosives, that is, a small amount of the primary explosive charge will easily detonate when subjected to a spark, flame, friction or a heated wire which will cause the explosive to reach its ignition temperature. The use of sensitive explosives in an ignitor causes several problems in that it is easily initiated by fires, heat, fragment impact and sympathetic detonation. This is a major safety concern particularly for military weapons.
Ignitors may also be of the two-stage variety wherein a primary explosive is used to ignite a secondary explosive which may then be used to ignite the propellant. The shockwave from the primary explosive and/or secondary explosive must be controlled so that the secondary explosive and the propellant itself are not expelled. Although the amount of primary sensitive explosive is reduced with this method, thereby reducing the resultant shockwave from an explosion of the sensitive explosive, this arrangement still has problems since there is ignition of the secondary insensitive explosive by a sensitive explosive. The safety problems are still present as the sensitive explosive could ignite from a slow cook off, fast cook off, sympathetic detonation, bullet impact, or fragment impact, thereby igniting the insensitive explosive.
Safety would be increased if the ignition of a propellant is accomplished using only insensitive explosives for detonation. However, problems arise when attempting to ignite the insensitive explosive and in confining and controlling the shockwave resulting therefrom. Insensitive explosives require a higher kinetic or thermal ignition energy, so that a typical bridge wire detonator may not have sufficient energy to cause the insensitive secondary explosive to detonate. In addition, if the resulting shockwave from the insensitive secondary explosive is too great, the propellant will be expelled without ignition as the shockwave passes through it. The energy from the shockwave must therefore be confined and dissipated to allow thermal or flame ignition of the propellant.
It can be seen then, that an initiator is required which does not utilize an explosively-sensitive material and which is ignited simply and safely. It can also be seen that an initiator is needed wherein the resulting shockwave from ignition of the insensitive secondary explosive is confined so that propellant is not expelled prematurely.